Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
To provide cellular wireless communication service, a wireless service provider or “wireless carrier” typically operates a radio access network (RAN) that includes a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) (also known as wireless communication devices (WCDs)) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the RAN may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
In general, a RAN may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1xRTT and 1xEV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handoff between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or blocks of frequencies (e.g., frequency bands, such as 698-960 MHz, 1610-2025 MHz, etc.) and may define a number of air interface channels for carrying information between the base station and UEs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing, for instance. By way of example, each coverage area may define a pilot channel, reference channel, or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that UEs may detect as an indication of coverage and may measure to evaluate coverage strength. As another example, each coverage area may define one or more uplink control channels or other resources on which UEs may transmit control messages to the base station. And each coverage area may define one or more downlink control channels or other resources on which the base station may transmit control messages or other information to UEs. Each coverage area may then define one or more traffic channels or other resource for carrying communication traffic such as voice data and other data between the base station and UEs.
When a UE first powers on or enters into coverage of the RAN and seeks to connect to a coverage area of the RAN, the UE may scan the pilot or reference signals of the RAN's coverage areas in an effort to determine a signal strength of each respective pilot or reference signal. The UE may then identify, for example, a coverage area with a strongest pilot or reference signal (e.g., having the highest signal-to-noise ratio) and may register with that coverage area by transmitting a registration request or attach request to a base station providing that signal and serving that coverage area. This registration process may serve to notify the RAN of the UE's presence in a particular coverage area and to facilitate network authentication of the UE. Once registered in that coverage area, the UE may then be served by the RAN in that coverage area in an “idle” mode in which the UE regularly scans for page messages and other overhead information from the RAN. Further, the UE may engage in additional signaling with the RAN in order to be served by the RAN in an “active” or “connected” mode in which the UE may then engage in bearer communication.
While a UE is served by a RAN in the idle or active/connected mode, the UE may also continue to scan the airwaves to help ensure that the UE continues to operate with the most optimal coverage. For instance, while operating on a particular carrier frequency in the UE's serving coverage area, the UE may continue to monitor the pilot signal or reference signals of that coverage area as well as the pilot signal or reference signals of adjacent coverage areas, and may at some point transmit to the serving base station or RAN a report indicating the strength of the monitored signals. For example, in an LTE system, the UE may transmit a radio measurement report to the RAN. After the RAN receives the report, the RAN may then use the report to provide the UE with preferable coverage. For instance, if the report indicates threshold low signal strength on the particular carrier frequency, the RAN may direct the UE to scan for coverage on one or more other carrier frequencies, such as another carrier frequency in the UE's serving coverage area or a carrier frequency in an adjacent coverage area. The RAN may then direct the UE to hand off to a given carrier frequency of the one or more other carrier frequencies so as to operate on the given carrier frequency.
In practice, the base stations of the RAN may not always provide seamless coverage throughout a region. As such, some network arrangements may include one or more wireless relays that extend the range of a base station's coverage area so as to partially or completely fill gaps in coverage and help improve service quality. A relay may be configured with a wireless backhaul interface for communicating with a base station in much the same way a UE does, and a wireless access interface for communicating with and serving one or more UEs in much the same way that a base station does. Further, the relay may include control logic for actively bridging the backhaul communications with the access communications. The relay may thus receive and recover downlink communications from the base station and transmit those communications to the UEs, and receive and recover uplink communications from UEs and transmit those communications to the base station. Advantageously, a relay like this can have a relatively small form factor, with antenna height lower than the base station and with reduced transmit power requirements.